Australian teenage girls have been warned over the dangers of painting their phone numbers onto their skin while they sunbathe on public beaches.

Child protection agencies said the stunt was likely to attract the wrong type of attention. [Agencies]

Groups of young girls have been photographed in bikinis with their mobile numbers written on their backs using blue-coloured zinc sunblock.

The 14 and 15-year-olds said they had travelled from Sydney's inner suburbs to Cronulla Beach in the city's south and Manly Beach in the north to "meet boys" and hoped the unusual tactic would encourage a few phone calls.

However, child protection agencies said the stunt was likely to attract the wrong type of attention.

One 15-year-old, identified only as Lizzy, admitted older men had been quickest to respond: "An old guy tried to talk to me. He was trying to take pictures of us," she told local newspaper The Manly Daily.

Child protection experts cautioned other teenagers against copying the stunt.

Girlforce author Nikki Goldstein said the practice was obviously dangerous.

"We'd never advise girls to broadcast their phone number anywhere that could make them a target," she told the Australian Daily Telegraph.

"They're in their bikinis, objectifying themselves is a bit trashy."

Psychologist Kirrilee Smout said the girls were too young to understand how to deal with the way some men would respond to the advertisements.